
const PENDING = 'pending'; //等待
const FULFILLED = 'fulfilled' //成功
const REJECTED = 'rejected' //失败
class MyPromise {
    constructor (executor) {
        try {
            executor(this.resolve, this.reject)
        } catch (e) {
            this.reject(e)
        }
        
    }
    //promise 状态
    status = PENDING
    //成功之后的值
    value = undefined
    //失败后的原因
    reason = undefined
    //成功回调
    successCallback = []
    //失败回调
    failCallback = []
    resolve = value => {
        //如果状态不是等待， 阻止允许
        if(this.status !== PENDING) return
        //将状态更改为成功
        this.status = FULFILLED
        //保存成功之后的值
        this.value = value
        //判断成功回调是否存在 如果存在 调用
        // this.successCallback && this.successCallback(this.value)
        while (this.successCallback.length)  this.successCallback.shift()()
    }

    reject  = reason => {
        //如果状态不是等待， 阻止允许
        if(this.status !== PENDING) return        
        //将状态更改为失败
        this.status = REJECTED
        //保存失败后的原因
        this.reason = reason
        //判断失败回调是否存在 如果存在 调用
        // this.failCallback && this.failCallback(this.value)
        while (this.failCallback.length) this.failCallback.shift()()
    }

    then (successCallback, failCallback) {
        successCallback = successCallback ? successCallback : value => value
        failCallback = failCallback ? failCallback : reason => {throw reason}
        let promise2 = new MyPromise((resolve, reject) => {
            //判断状态
            if(this.status === FULFILLED) {
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断x 的值是普通值还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve 还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }, 0);
            } else if(this.status === REJECTED) {
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason)
                        // 判断x 的值是普通值还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve 还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }, 0);
            } else {
                //等待
                //将失败回调和成功回调存储起来
                this.successCallback.push(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断x 的值是普通值还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve 还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }
                }) 
                this.failCallback.push(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断x 的值是普通值还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve 还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (e) {
                        reject(e)
                    }                    
                })

            }
        })

        return promise2
    }

    finally (callback) {
        return this.then(value => {
            callback()
            return value
        }, reason => {
            callback()
            throw reason
        })
    }

    static all (array) {
        let result = []
        let index = 0
        return new MyPromise((resolve, reject) => {
            function addData (key, value) {
                result[key] = value
                index ++
                if (index === result.length) resolve(result)
            }
            for (let i = 0; i < array.length; i++) {
                let current = array[i]
                if(current instanceof MyPromise) {
                    current.then(value => addData(i, value), reason => {
                        reject(reason)
                    })
                } else {
                    addData(i, current)
                }
            }
           
        })
    }

    static resolve (value) {
        if (value instanceof MyPromise) {
            return value
        } else {
            return new MyPromise(resolve => resolve(value))
        }
    }
}

function resolvePromise(promise2, x, resolve, reject) {
    if(promise2 === x) return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
    if(x instanceof MyPromise) {
        //promise 对象
        //x.then(value => resolve(value), rason => reject(reason))
        x.then(resolve, reject)
    } else {
        //普通值
        resolve(x)
    }
}

module.exports = MyPromise